Art of preventing corrosion of apparatus for distilling hydrocarbon oils



1935- w. G. WHITMAN 1,986,236

ART OF PREVENTING CORROSION 0F APPARATUS FOR DISTI LLING HYDROCARBON OILS Filed June 26, 1950 2 Sheets-Sheet 1 Q fzverzi or. N Eifer amiivnan l I J I kfl Jan. 1, 1935. w, G. WHITMAN 1,986,236

ART OF PREVENTING CORROSION OF APPARATUS FOR D ISTILLING HYDROCARBON OILS Filed June 26, 1930 2 Sheets-Sheet 2 Patented Jan. 1, 1935 UNITED STATES ART OF PREVENTING CORROSION OF APPARATUS FOR" DISTILLING HYDRO- CARBON OILS Walter G. Whitman, Whiting, Ind., assignor to Standard Oil Company, Whiting, 11141., a corporation of Indiana Application June 26, 1930, Serial No. 463,939

8 Claims.

This invention relates to the art of preventing corrosion of apparatus employed in the distillation of hydrocarbon oils.

The invention will be fully understood from the 6 following detailed description in conjunction with the accompanying drawings, in which:

Figure 1 is a somewhat diagrammatic elevational view of apparatus suitable for carrying out the present invention;

Figure 2 is an enlarged vertical sectional view of a device for admixing steam with the oil; and

Figure 3 is an enlarged vertical longitudinal sectional view of the pipe still furnace shown in Fig. 1.

In the distillation of petroleum oils, and especially crudes, reduced crudes, and other petroleum fractions for the separation of various fractions therefrom, it is the practice to bring steam into admixture with the body of such oil undergoing distillation. Such use of steam materially aids vaporization of the fractions which it is desired to distill off and causes them to separate from the liquid oil at temperatures considerably lower than is the case when steam is not so used. This use of steam is particularly desirable in the distillation of lubricant fractions from reduced crudes or other lubricant containing stock, as

the distillation may be conducted at a temperature below that at which serious cracking or decomposition occurs.

It is often the practice to bring the oil undergoing distillation substantially to the temperature at which it is to be distilled before steam 1s introduced into the oil to aid vaporization. This type of operation is usually employed when distillation is effected by means of a pipe still, as the premature introduction of steam during the heating of the oil causes a substantial pressure drop in the still and if said pressure drop is avoided by supplying several parallel tubes for the flow of oil, the mass velocity is so reduced that the coeflicient of heat transfer is too low for safe operation at high rates of heat input and local overheating of the pipe still results. Hence, it is the practice when distillation is effected by means of a pipe still, to introduce the steam into the stream of oil at a point where it has reached, or has'almost production of lubricants. The rate of corrosion ordinarily increases with the increase of temperature. Thus, when operating a pipe still for the distillation of lubricant oils, I have found that an undesirable amount of corrosion occurs in the metal parts of the still wherein the oil stream has not yet reached a temperature at which it is advantageous to 'admix steam with it for the purpose of aiding vaporization.

I have found that such corrosion may be substantially entirely prevented by admixing small portions of steam or water with the oil in quantities insuflicient to effect material vaporization of the oil. It has been found that the amount of water or steam required is relatively small, for example, about one twentieth of the amount of steam or water necessary to aid vaporization, in the manner heretofore described, will efiectively prevent corrosion of the metal parts of the still. The amount of water or steam necessary to prevent such corrosion ordinarily is between 0.05 and 0.4 lbs. per gallon of oil.

The minimum temperature at which this small amount of water or steam is introduced, varies with the particular oil being treated. The water or steam should be admixed with the oil between the minimum temperature and 650 F. For example, with a 22 A. P. I. reduced Winkler crude, the water or steam-should be added when or before the oil reaches a-temperature between' 450 and 600 F., and preferably when or before it reaches a temperature of approximately 525 F. Such minimum temperature may be determined by observing at what temperature a substantial amount of hydrogen sulfide gas is evolved from the oil, as experimental data has led me to believe that the presence of such gas causes a substantial amount of corrosion of the metal in contact with the oil. In general, it may be said that the water or steam ordinarily should be introduced into the oil for corrosion preventing purposes when or before the oil reaches 525 F.

Referring now in detail to the drawings, and particularly to Fig. 3, the numeral 5 indicates a pipe still furnace layout, 6 being a combustion chamber provided with a burner '7 and divided by a bridge wall 8 from a convection section 9 through which extends a plurality of series connected pipes 10 and a plurality of parallel banks 11 of serially connected pipes 12. The upper portion of the furnace is.provided with a plurality of serially connected pipes 13 which are exposed to the radiant heat within the furnace, and which are connected to the outlet of the serially connected pipes 10 by means of a line 14. shown diagrammatically in Fig. 1. The pipes are connected to a charging line 15. A valved outlet line 16 leads from the pipes 13 in the upper portion of the furnace and discharges into the upper portion 0 i a surge tank 17. The surge tank is provided with a valved oil discharge line 18 leading to a header 19 and a valved vapor discharge line 20 leading to a header 21. A valved steam line 22' is connected to the vapor header 21 and a valved line 23 connects the outlet line 16 from pipes 13 with the oil header 19. A valved line 24 communicates with the vapor space in the surge tank 1'7 and is connected to the oil header 19.

For each bank 11 of tubes 12 a mixer.25 is provided, each mixer 25 being connected to one of the banks 11 of tubes 12 by means of separate lines, 26. Each mixer 25 is connected to the vapor header 21 by means of separate valved lines 27 and each mixer is connected to the oil header 19 by separate valved lines 28. A valved steam supply line 29 and a valved water line 30 are connected to a valved line 31 which discharges into the line 14 connecting pipes 10 and 13 within the furnace 5. Thebanks 11 of tubes 12 discharge into a header 29' through a plurality of separate lines 30'. I I

In an operation in connection with the above described apparatus, 125 bbls. per hour of 22 A. P. I. reduced Winkler crude were charged through line 15. The oil was passed through the lower section of tubes 10 where it received heat from combustion gases in section 9 and then through the line 14 and through tubes 13 in the upper portion of the furnace where it received mainly radiant heat.

The oil while passing through pipes 13 was 7 brought substantially to a temperature at which it is desired to effect distillation of the lubricant therefrom with the aid of steam. Under the existing pressure, which is essentially that required to overcome frictional resistance to flow through the pipes, although it may be higher, some vaporization may occur'without the aid of steam and may tend to cause slugs of vapor and liquid to form within the pipes, particularly when steam for vaporizing purposes is introduced into the oil stream. It is desirable, therefore, to thoroughly and uniformly admix the oil with the steam, together with any vapors that may have formed in the still. To this end, the oil is passed from pipes 13 through line 16 and into surge tank 17 wherein any vapor and the unvaporized oil are separated, the separated vapors being passed from -the surge tank 17 to vapor header 21 through line 20 and the unvaporized oil being passed to oil header 19 through line 18.

Steam in an amount suflicient to materially aid vaporization of the oil is introduced into vapor header 21 through line 22. Ordinarily about 2 lbs. of steam per gallon of oil is sufficient to effect the desired vaporization.

Oil is supplied to each mixer 25 through lines 28 and vapor and steam are so supplied through lines 27. The steam, vapor and unvaporized oil are thoroughly admixed within mixers 25, each mixer discharging such mixture through one of the lines 26 leading to thebanks 11 of pipes 12. Thefeed of the oil in each mixer 25 is facilitated by the aspirating action of the current of vapors passing therethrough. The mixture of steam, vapors and oil receives heat from combustion gases while flowing through the banks of parallel pipes 12 and vaporization of the lubricants occurs. The oil is then discharged into a header 29- through which the oil passes to a flash drum (not shown) or other suitable separating or fractionating device, wherein the desiredfractions sepa-- rate as vapors.

The line 24 functions to equalize pressure conditions and the-valve therein is kept open when the surge tank is so used.

The above described type .of operation is fol- I lowed when vaporization has occurred to such an extent that slugs of vapor and liquid are liable to form on further passage of the oil through the still. The still may be operated without the use of the surge tank 17. To accomplish this, the valve 31 in line 16 is closed as well as valves 32, 33 and 34 in lines 20, 24 and 18, respectively, and valve 35 in line 23 is opened to permit the oil from pipes 13 to flow directly into header 19. Steam alone is then supplied to header 21, and the oil and such steam are admixed in mixers 25 and passed to the pipes 12 for parallel flow through the furnace 5.

I have found that in the above operations that very little corrosion occurs in the pipes 10 and the various valves, fittings and, other metal parts which are associated therewith. However, I find that serious corrosion occurs within the tubes 13 where the oil reaches a higher temperature. I have found that the addition of a small quantity of water, i. e., from 0.05 to 0.4 lb. and preferably from 0.1 to 0.2 lbs. per gallon of oil, either in the.

form of liquid or steam, to the oil stream before it enters pipes 13 substantially entirely prevents corrosion of the pipes 13. The water or steam may be introduced into the oil stream before it reaches the tubes or pipes 13 by means of lines 29, 30 and 31. Such a small amount of water does not cause substantially any increased vaporization in the tubes 13 during the heating of the oil therein, and hence the rate of heat transfer and pressure conditions are substantially unaffected.

In the above described operation, the oil was charged into the pipe coil 10 at a temperature of 430 F., entered pipe-coil 13 at 510 F. and was discharged into line 16 at 740 F. The steam and oil mixture was heated to 750 F. in the vaporizing pipe-coils 11.

While I have described an operation in'which small quantities of water, or steam, are employed in an amount insufllcient to materially increase vaporization in a distillation process carried out by means of a pipe still, it is to be understood that the present invention is equally applicable to such distillation in other apparatus where similar dimculties arise. It is to be understood that the term aqueous fluid as employed in the following claims includes water in the form of steam as well as liquid and the term water is generic to water in liquid form or in the 'form of steam. The specific details of the process and apparatus above set forth are not intended to be regarded as limitations upon the scope of the invention, except insofar as included in the accompanying claims.

I claim:

1. 1n the art of pipe still distillation of petroleum oils, wherein oil is passed in a metal conduit means through successive heating zones in the first of which zones it is heated mainly by combustion gases and in the second of which zones it receives radiant heat before substantial vaporization occurs, the method of-preventing corrosion of the metal conduit means which conducts the oil through said second heating zone which compr ses, injecting aqueous fluid into the oil after initially heating the oil but before it enters the second heating zone in an amount insumcient to materially aid vaporization of the oil during its flow through the said second zone.

2. In the art of pipe still distillation of petroleum oils, wherein oil is passed in a metal conduit means through successive heating zones in the first of which zones it is heated mainly by combustion gases and in the second of which zones it receives radiant heat before substantial vaporization occurs, and steam is added to the oil after it leaves the second heating zone in an amount sumcient to materially aid vaporization of the heated oil, the method of preventing corrosion of the metal conduit means which conducts the oil through said second heating zone which comprises, injecting aqueous fluid into the oil after initially heating the oil but before it enters the second heating zone in an amount insuiiicient to materially aid vaporization of the oil during its flow through the said second zone.

3. In the art of pipe still distillation of petroleum oils, wherein oil is passed in a confined stream within a metal conduit through successive heating zones in the first and third of which zones it is heatedmainly by combustion gases, in the second of which zones it receives radiant heat, and steam is added to the oil after it leaves the second zone and before it enters the third heating zone in an amount sufilcient to materially aid vaporization of the oil, the method of preventing corrosion of the metal conduit means which conducts the oil streamthrough the second heating zone which comprises, injecting aqueous fluid into the stream of oil just before it enters the second heating zone in an amount insumcient to materially aid vaporization of the oil.

4. In the art of pipe still distillation of petroleum oils, wherein oil is passed in a confined stream within a metal conduit through successive heating zones in the first and third of which zones it is heated mainly by combustion gases, in the second of which zones it receives radiant heat, and steam is added to the oil after it leaves the second zone and before it enters the third heating zone in an amount sumcient to materially aid vaporization of the oil during its flow through the third heating zone, the method of preventing corrosion of the metal conduit means which conducts the oil stream through the second heating zone which comprises, injecting aqueous fluid into the stream of oil just before it enters the second heating zone in an amount insufflcient to materially aid vaporization of the oil.

5. In the distillation of petroleum oils in metal conduits to obtain lubricant fractions of oils, the steps comprising heating the petroleum oils in the absence of aqueous fluid to a temperature of about 400 F., admixing with the thus heated oils quantities of aqueous fluid in amounts ranging from 0.05 to 0.4 pounds per gallon of oil to prevent corrosion of the metalconduits in contact with the heated oils above 400 F.

6. In the art of obtaining lubricant fractions of oil by distilling petroleum oils, in contact with which the metal walls of distillation apparatus tend to corrode, the improvement which comprises heating the oil in the absence of aqueous fluid within metal conduits to about 400 F., then admixing an aqueous fluid with the hot oil. in amounts not exceeding 0.4 pounds per gallon of oil in order to prevent corrosion of the metal conduit in contact with the oil at higher temperatures and further heating the admixture in metal conduits to higher temperatures.

7. In the art of pipe still distillation of petroleum oils without substantial cracking and in the absence of suflicient amounts of aqueous fluid to efiect substantial increased vaporization of the oils, wherein the oils flow in a restricted stream confined in an externally heated metal conduit and are therein heated to a temperature at which substantial vaporization of the oils is effected, the method of preventing corrosion of the metal surface in contact with the oils undergoing such heating where the corrosion tends to become marked which comprises supplying aqueous fluid to the stream of oil undergoing such heating in an amount ranging from 0.05 to 0.4 pounds per gallon of oil and at a point where the oil has reached a temperature of about 400 F.

8. In the art of distilling, without substantial cracking, petroleum oils containing constituents which cause corrosion of metal walls of the distillation apparatus in the course of the distillation, the improvement which consists in heating said oils to a temperature of about 450 F. in the absence of aqueous fluid and thereafter introducing steam into the oil at a point where corrosion of the metallic wall surfaces in contact with the heated oil tends to become marked, said steam being introduced in amounts between about 0.05 and 0.4 pounds per gallon of oil.

WALTER G. WHITMAN. 

